1. Field of the Invention
The present invention relates to organopolysiloxane-containing compositions based on water, which are essentially free from organic solvents, have a flash point of more than 70.degree. C. and liberate essentially no alcohols by hydrolysis on dilution with water, to a process for their preparation and to their use.
2. Description of the Background
Organosilanes of the formula R.sup.0 --Si(OR.sup.1).sub.3, where R.sup.0 is an organic radical and R is a methyl or ethyl radical, have diverse uses, for example as adhesion promoters, release agents, rheology improvers, crosslinking agents and hydrophobizing agents.
For ecological, industrial safety and economic reasons, there is an ever increasing trend to use the organosilanes in aqueous form. The following problems generally arise here.
(i) Alcohols are liberated by hydrolysis: EQU R.sup.0 --Si(OR.sup.1).sub.3 +3 H.sub.2 O--R.sup.0 --Si(OH).sub.3 +3 R.sup.1 OH
Free alcohols lower the flash point of the solution used, so that explosion-protected machines and special apparatuses must be employed for the necessary processing steps. For toxicological reasons, employees entrusted with handling the substances must be additionally trained and protected. Furthermore, disposal of the spent solution used may present difficulties because of the hydrolysis alcohols. Special wastewater clarification units and also units for after-treatment of waste gas and waste air are required.
(ii) The organosilane to be applied in water is not water-soluble: EQU R.sup.0 --Si(OR.sup.1).sub.3 +1.5 H.sub.2 O--R.sup.0 --SiO.sub.1.5 +3 R.sup.1 OH
The hydrolysate R.sup.0 --SiO.sub.1.5 formed by this reaction precipitates out of the reaction mixture as polymeric silicone resin, so that it is no longer available for the desired use. Although organosilanes having a very highly hydrophobic character, such as, for example, alkylalkoxysilanes, especially those having a long, branched carbon skeleton or optionally having fluorinated alkyl groups, such as are described, for example, in German Patent Application No. 196 44 561.2, hydrolyze or condense very slowly, they are not soluble in water and, after hydrolysis, are chiefly present as polymeric silicone resin which is not water-soluble.
In recent years, a large number of new fields of use have been found for fluoroalkylchlorosilanes and fluoroalkylalkoxysilanes. These compounds are thus employed, for example, as additives in surfactants, as lubricating agents, for the surface-coating of lenses or optical fibers, as primers for fluorinated resins, as constituents of cosmetic formulations, as a modifier in fluorinated rubbers and silicone rubbers and for the production of oil-, dirt and water-repellent surfaces. Such organosilanes as a rule cannot be used or can be used only with disadvantages in aqueous applications, although there is an increasing demand for just such applications. Thus, for example, in the textile and leather industry, surface treatments from aqueous solution are desired objectives. A clear trend toward the use of water-based systems is desired for the impregnation of mineral surfaces, for example, the building facades of plaster, concrete, lime sandstone, brick or other mineral building materials, in the buildings protection sector. Oil- and water-repellent coatings on surfaces, usually glass surfaces, are essentially produced with the aid of fluoroalkylalkoxysilanes and fluoroalkylchlorosilanes (European Laid-Open Application No. 0 629 673 and European Laid-Open Application No. 0 658 525). Such coatings can also be used for the provision of plate glass with a dirt-repellent treatment. The processes described are based on sol-gel processes, in which very fine inorganic particles being produced and employed together with the fluoroalkylsilane employed. The application is technically demanding, and usually uses complex organic solvent mixtures and additives.
Alcoholic solutions based on fluoroalkylalkoxysilanes for producing oil- and water-repellent coatings are known as described in U.S. Pat. No. 5,424,130, such solutions having high alcohol contents of, for example, 52% by weight of ethanol.
In the processes described, the complicated application processes on the one hand and the use of organic solvents on the other hand have adverse effects. In some processes, even substances which are very problematic ecologically, such as chlorinated hydrocarbons or fluorohydrocarbons, are employed as solvents in a considerable concentration (European Laid-Open Application No. 0 491 251 and European Laid-Open Application No. 0 493 747). Furthermore, silanes containing fluoroalkyl groups are very expensive substances. There is, therefore, certainly an economic interest in achieving savings on silanes which contain fluoroalkyl groups, for example, by replacing silanes which contain fluoroalkyl groups by alkylsilanes, virtually as a dilution medium, which could have the result of increasing the hydrophobizing action for the same amount of fluoroalkylsilane employed.
In order to mitigate the known disadvantages described above, the most diverse processes have been suggested in the past.
In the emulsion method, the organosilane, which is not compatible with water per se and is a liquid silicone resin which is not water-soluble, is emulsified in water with the aid of emulsifiers (European Laid-Open Application No. 0 442 098, European Laid-Open Application No. 0 358 652 and U.S. Pat. No. 4,620,878). A disadvantage with this method is that the products comprise noticeable proportions of surfactants as emulsifiers and can liberate considerable amounts of alcohol.
Removal of hydrolysis alcohols by distillation during synthesis of organosilane formulations from water-soluble organosilanes, such as, for example, from 3-aminopropyltriethoxysilane, is known. Aqueous aminosilane systems which have a low alcohol content and are otherwise solvent-free are accessible in this manner and are available on the market, for example in the form DYNASYLAN.RTM. 1151.
Although some organosilanes such as, for example, aminoalkylalkoxysilanes. are stable in aqueous solution they can be used to only a limited extent for the diverse possible uses of organofunctional silanes. The addition of further organic functionalities per se in an aqueous solution of non-stable organosilanes, in particular in a relatively high concentration, can result in a formulation with particular properties or with a combination of hitherto unknown properties.
A formulation of silane combinations in water is known as disclosed U.S. Pat. No. 5,073,195. The silane formulations are prepared from an alkyltrialkoxysilane which is not water-soluble and a water-soluble silane, such as, for example, an aminoalkylalkoxysilane, in a molar ratio of 1:2-3:1. As can be seen from the examples of the U.S. patent, the formulations are prepared by hydrolysis of the silane mixture in less than the stoichiometric ratio and removing volatile materials of the reaction mixture at 60.degree. C. under reduced pressure, and for subsequent uses the silane formulations thus obtained are also diluted with water. As a result of dilution with water, however, the alkoxy groups which remain, as a result of incomplete hydrolysis, are then split off in the form of the corresponding alcohols. The silane cohydrolysates disclosed thus comprise free alcohols in significant amounts, and can moreover liberate further amounts of alcohol by hydrolysis, and contain no Si compounds which carry fluoroalkyl groups, which means that the application properties of the products are adversely affected in comparison to the products of the invention.
European Patent Application No. 0 675 128 describes the modification of water-based organosilane formulations with small amounts of organosilanes which are not water-soluble per se, such as, for example, methyltrimethoxysilane or vinyltrimethoxysilane. In fact, a molar ratio of the component, which is not water-soluble, to the water-soluble component of 1:2.5 is possible. With a higher proportion of silanes which are not water-soluble, highly viscous products which gel in the course of time are formed. The application properties of the formulations prepared essentially correspond to those of the above-mentioned aqueous organosilane formulations. Aqueous solutions which have relatively high contents of organosilanes, which are not water-soluble, for example methacryloxypropyltrimethoxysilane, and are stable for months are not accessible by this process. The preparation of purely aqueous solutions using silanes which have a highly hydrophobic action, such as, for example, isobutyl- or octyltrimethoxysilane, is also certainly not possible in this manner.
European Laid-Open Application No. 0 716 127 and European Laid-Open Application No. 0 716 128 disclose the preparation of water-soluble, solvent-free organosilane formulations which are essentially free of hydrolysis alcohols and have high contents of silanes which are not water-soluble, inter alia, alkylsilanes, vinylsilanes and ureidosilanes. The water-solubility of the formulations is achieved by controlled cohydrolysis of aminosilanes with silanes which are not water-soluble, subsequent neutralization of the amino functional group with acids, and distillation of the hydrolysis alcohols. A need continues to exist for a solvent free, aqueous organosilane containing composition which is useful in a variety of coating and substrate treatment applications.